In a known design of starter contactor, the contactor is controlled by an electromagnetic auxiliary relay which enables commands for controlling the contactor to be transmitted by means of a low current. As a result, the ignition switch of the vehicle no longer has to support a current of high intensity, which may typically be several tens of amperes: a current of the order of 1 ampere is perfectly sufficient to insure proper control of the contactor. Thanks to this arrangement, it is possible to reduce the dimensioning of the wiring and of the ignition switch associated with the ignition key.
In addition, a starter having an auxiliary control relay for the contactor can be governed easily and inexpensively by an electronic control circuit which may, in particular, take into account information relating to the locking of the steering lock of the vehicle, and which can include a control and safety system which takes care of any electrical overloads occurring in the operation of the starter.
In known designs, the auxiliary relay is typically fixed outside of the contactor, e.g. on the contactor itself; the relay may for example be carried on the starter casing or on the pedestal of the starter motor, or on an element of the bodywork of the vehicle.
In all the above mentioned cases, the auxiliary control relay has its own protective housing, with its own sealing means and its own wiring by which it is connected electrically to the control circuit and to the contactor. These designs therefore lead to particularly high costs, and to additional space requirements in the engine compartment of the vehicle.
With a view to incorporation of the relay within the contactor, and in order to overcome the problems just mentioned, it has previously been proposed to provide a contactor in which the end cap or cover of the contactor casing includes a chamber in which the auxiliary control relay is mounted. This design does enable the auxiliary relay to be protected, and reduces the length required for the various connecting cables.
In order to improve still further the incorporation of the auxiliary control relay into the contactor, it was proposed in French patent specification No. FR 2 724 421 A to provide a contactor which includes an auxiliary electromagnetic control relay mounted in the chamber in the end cap, between the fixed core and the movable contact of the contactor. The auxiliary relay includes a relay coil of generally annular form, within which a movable relay core is guided in axial sliding movement. The control rod extends through the centre of this movable relay core, and the latter carries a movable relay contact ring which, under the action of the relay coil, is adapted for cooperation with at least one pair of fixed relay contacts carried by a fixed, annular, contact carrier plate of insulating material. The contactor is further of a type in which the movable relay core is biassed resiliently towards an axial rest position.
In the design proposed in the above mentioned French patent specification, the auxiliary control relay, which generally has the form of a body of revolution, and through which the control rod for the movable contact of the contactor passes, is made in the form of a separate, attached, sub-assembly which is fixed by means of screws on the fixed magnetic core of the contactor.
Apart from the fact that the specific assembly operations for fitting the auxiliary control relay on the contactor are relatively complex, this design, taking the form of an independent component fitted in the interior of the contactor, results in a significant increase in the axial length of the contactor and also in its weight.
In addition, the detail design of the auxiliary control relay proposed in the above mentioned French patent specification makes it necessary, in order to determine the rest position of the movable contact ring of the auxiliary control relay, to make use of a stack of opposed springs, with precise axial dimensioning of the various components. It is therefore particularly difficult to determine reliably the axial rest position of the movable relay contact, and such a design makes it necessary to manufacture certain of the components of the auxiliary relay with very great precision.